Green Mountain Coffee Roasters Inc., the small Vermont company that hit it big as king of the single-serve home brew, is booming again thanks to its new partnership with the Coca-Cola Co. to develop the next generation of cold drinks.

Green Mountain stock soared Thursday, a day after the company announced an agreement for Coca-Cola to invest $1.25 billion for a 10 percent stake in its business. The companies signed a 10-year partnership agreement to develop Coke’s beverages for Keurig’s yet to be released single-serve cold drink system.

The arrangement gives Green Mountain a powerful partner in a new line of business that will help it expand beyond the maturing single-serve coffee market. Coca-Cola is gaining a foothold in the fast-growing market for homemade cold drinks, from sodas to teas and juices.

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“The fact that Coca-Cola is signing a 10-year deal on a product that won’t be on the market for a year is almost unheard of,” said Scott Van Winkle, a Boston analyst with Canaccord Genuity. “Coca-Cola sat down at the home beverage table and went all in on the first hand.”

Green Mountain shares soared $21.22 to $102.10 on Thursday, jumping more than 26 percent on the news of the Coca-Cola investment. The one-day increase boosted the market value of the company by more than $3 billion.

The expansion into cold beverages is an obvious growth opportunity for Keurig, the runaway leader among the makers of single-cup coffee brewing systems used in offices and homes. So far, the market has been dominated by SodaStream, an Israeli company that recruited A-list actress Scarlett Johansson for a 30-second Super Bowl spot to help it push into the US market.

SodaStream carbonated beverage machines are widely available in American stores, retailing at prices from $79.99 to $129.99. The company has partnerships with brands like Ocean Spray, Crystal Light, and Kool-Aid.

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Brian Kelley, chief executive of Green Mountain, said that unlike SodaStream, Keurig Cold will deliver carbonated beverages without CO2 cartridges. Customers also won’t have to calculate the carbonation or syrup for each drink because the recipes are built into the system. He declined to say how much Keurig Cold equipment will cost.

In addition to sodas, Keurig Cold will serve enhanced waters, juices, sports drinks, and teas with the same one-touch method as the Keurig coffee brewers. The machine will debut in 2015 with a full suite of Coca-Cola branded cups, which could include anything from Sprite, Minute Maid, and Fanta to Hi-C.

“Coca-Cola has the best portfolio of beverage brands, a distribution system that is unparalleled, and expertise globally in the beverage business,” Kelley said in an interview Thursday. “We bring innovative break-through technology, the strong Keurig system, and that in-home consumer experience. It makes for the perfect combination.”

Kelley believes the cold beverage system will appeal to a more global audience than the Keurig coffee brewers and boost the company’s expansion.

Coffee preferences vary country by country, he said, and it’s difficult to build a brand or system that appeals to everyone around the world. But cold beverages like Coca-Cola are consumed the same way all over the globe.

“The cold beverage business has built brands that are global,” Kelley said. “Our initial focus will be in North America and then we’ll expand around the globe.”

Green Mountain started in 1981 as a small cafe serving coffee to diners in Waitsfield, Vt. The company first invested in Keurig in 1993. Green Mountain acquired the Massachusetts company in 2006 and rode the boom in single-serve coffee brewers into more than 15 million American households.

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But Green Mountain has had its share of critics in recent years. The company has been dogged for several years by short sellers who claimed that expiring patents and questionable accounting would eventually drive Green Mountain’s stock price lower.

Critics shorted the stock, taking positions that would make money if and when the shares declined in value. More than 35 million Green Mountain shares — nearly one of every three available for trading — had been sold short as of last month.

Billionaire hedge fund manger David Einhorn has been the most visible Green Mountain short seller, writing letters and making investment presentations criticizing the company.

Analysts said the naysayers were all but silenced this week when Coca-Cola agreed to buy more than 16 million shares for $74.98 each of a stock that had fallen under $20 just a year and a half ago.

“Before [Wednesday] we didn’t know what if anything would come from the cold beverage system,” said Jonathan Feeney, a food and beverage analyst with Janney Capital Markets. “Now we know the leading beverage company in the US is partnering with them to get it started and is making a significant investment. Its caught a lot of people by surprise.”